The distribution and type B trichothecene chemotype of Fusarium species associated with head blight of wheat in South Africa during 2008 and 2009

Fusarium head blight (FHB) of wheat occurs commonly in irrigation regions of South Africa and less frequently in dryland regions. Previous surveys of Fusarium species causing FHB identified isolates using morphological characters only. This study reports on a comprehensive characterisation of FHB pathogens conducted in 2008 and 2009. Symptomatic wheat heads were collected from the Northern Cape, KwaZulu-Natal (KZN), Bushveld and eastern Free State (irrigation regions), and from one field in the Western Cape (dryland region). Fusarium isolates were identified with species-specific primers or analysis of partial EF-1α sequences. A representative subset of isolates was characterized morphologically. In total, 1047 Fusarium isolates were collected, comprising 24 species from seven broad species complexes. The F. sambucinum (FSAMSC) and F. incarnatum-equiseti species complexes (FIESC) were most common (83.5% and 13.3% of isolates, respectively). The F. chlamydosporum (FCSC), F. fujikuroi (FFSC), F. oxysporum (FOSC), F. solani (FSSC), and F. tricinctum species complexes (FTSC) were also observed. Within the FSAMSC, 90.7% of isolates belonged to the F. graminearum species complex (FGSC), accounting for 75.7% of isolates. The FGSC was the dominant Fusaria in all four irrigation regions. F. pseudograminearum dominated at the dryland field in the Western Cape. The Northern Cape had the highest species diversity (16 Fusarium species from all seven species complexes). The type B trichothecene chemotype of FGSC and related species was inferred with PCR. Chemotype diversity was limited (15-ADON = 90.1%) and highly structured in relation to species differences. These results expand the known species diversity associated with FHB in South Africa and include first reports of F. acuminatum, F. armeniacum, F. avenaceum, F. temperatum, and F. pseudograminearum from wheat heads in South Africa, and of F. brachygibbosum, F. lunulosporum and F. transvaalense from wheat globally. Potentially novel species were identified within the FCSC, FFSC, FOSC, FSAMSC, FIESC and FTSC.

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Introduction 46 Fusarium head blight (FHB) is a major disease of wheat (Triticum aestivum) worldwide. The disease reduces grain yield and causes the production of discoloured, shrivelled kernels 48 contaminated with mycotoxins [1]. In the late 1990s, FHB resulted in losses estimated at US$ 2.7 49 billion in parts of the USA [2], while about 7 million ha have been affected by FHB epidemics in China 50 [3]. The disease has also been damaging to wheat production in South America [4 -7], Canada [8, 51 9] and Europe [10,11]. In South Africa, wheat production has been negatively affected by the 52 disease, although little information is available on its financial impact.   where 40 symptomatic wheat heads were randomly sampled from the spring cultivar SST027.

Geographical distribution of Fusarium species 321
The FGSC and FIESC were the most widely distributed fusaria in South Africa (Fig 1). The

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FGSC was found in all production regions and localities, apart from Modderrivier (Northern Cape)

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The Northern Cape was the wheat production region with the highest FHB species diversity,

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Fusarium species other than those in the FGSC and FIESC were mostly obtained at low 371 incidences (

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Fusarium isolates collected in South Africa (S1 Table). Isolates with the 3-ADON and NIV types 395 comprised 5.4 and 4.5%, respectively, of the FSAMSC-1 isolates in the country. The 15-ADON type 396 was only observed among the FGSC, where it was predominant (97.4%). Less than 0.5% of this 397 species complex had the 3-ADON type, while 2.3% had the NIV type (S1 Table).

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Isolates with known type B trichothecene chemotype identities were provided by Laëtitia

Identification of Fusarium isolates 213
Single-spore cultures were grown on PDA plates for 7 days, where after genomic DNA was 214 extracted from mycelia using the Wizard® SV Genomic DNA Purification System Kit (Promega, multiplex PCR with known species-specific primers (

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[59], and the FGSC species will therefore not be referred to by their phylogenetic species names.

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The molecular identities of FHB isolates from South Africa were linked to prior morphological species